The present invention relates to a digital burst signal transmission system for use in a multi-directional time division multiplex (MD-TDM) communication system for a point to multipoint communication and a time division multiple access (TDMA) communication system for a multipoint to multipoint satellite communication.
In a MD-TDM communication system, a central station (master station) transmits signals to peripheral stations (slave stations) on a time division basis, and each slave station picks up only the signals within the time slots assigned to it out of all the signals transmitted from the master station. Each slave station transmits burst signals to the master station within the time slots allocated thereto. In a TDMA communication system, on the other hand, many earth stations transmit and receive burst signals in a time division format via one satellite. Such burst signals can be obtained, for instance, by gating a modulated carrier wave. However, since this gating is achieved without regard to frequency spectrum, there occur steep discontinuations of the carrier wave at its leading and trailing edges. This results in a spread of the frequency spectrum and impulse interference with the adjoining frequency (or channel). Furthermore, the interfering impulse usually affects the channels of other systems at random, inviting deterioration of the code error rate.
Conventionally, this spectral spread has been prevented by the so-called roll-off waveform shaping with a transmission filter. However, since this waveform shaping adversely affects the waveform of the input pulse signal at both edges of a burst signal, if plural burst signals are to be sequentially transmitted, a code interference is unavoidable between the burst signals with the result that a few time slots are lost during which no information can be transmitted.